On behalf of my fellow colleagues at
Entegris, I am writing to share with you how excited we are to join forces with Versum Materials. We believe the merger between Entegris and Versum Materials will create a company better equipped to help our customers solve their most complex
manufacturing process challenges, faster and more efficiently than ever before. Together, we will be able to offer our customers unique insight gained from a highly diversified solutions portfolio, greater access to industry expertise across a wider
global presence, more state-of-the-art labs and capabilities, and an unmatched commitment to ongoing innovation funded by a
partner with sound financial stability.

As you know, semiconductor demand is accelerating driven by radical technologies of The Fourth Industrial
Revolution, such as artificial intelligence, IoT, VR, and cloud computing. The compute power needed to fuel these applications relies on higher performance advanced logic and memory chips in much greater quantities. Entegris operates at the
intersection of materials and purity  this is the right time and the right area for us to grow our business and we believe Versum is the right partner. To say I am confident that this combination will create great opportunities for our
companies, our employees, and our customers is an understatement.

One thing you may not know about Entegris is that we have a long, rich history of
merger success. In fact, I joined Entegris in 2005 as part of the merger with Mykrolis, which in an interesting parallel had been spun out of Millipore just five years earlier. This is not a unique story at Entegris, there are many employees from
Mykrolis, POCO Graphite, and ATMI  including half of our executive team, who after coming to Entegris through M&A activities have grown successful careers. It is important for you to understand this is a merger predicated on growth, and I
am exhilarated by the prospect of what our employees can accomplish together.

A critical factor to our continued success is you. Your innovative
thinking, strong execution, and relentless focus on customer success has positioned Versum as a cutting-edge specialty materials supplier. We will rely on you to continue providing customers with the same outstanding service and high-quality
products and solutions that they have come to expect.

Successfully bringing our two companies together will require a thoughtful integration plan. To
help facilitate this effort, we are creating an Integration Planning Office consisting of individuals from both companies. We will be communicating more about that team and their plan soon. In the coming days, I will be hosting a global town hall
meeting from the Tempe office on February 11th to tell you more about Entegris, and I look forward to meeting and speaking with as many of you as possible.

Until then, let me reiterate the admiration of the collective Entegris team and thank you in advance for your patience and continued focus on customer success
as we move toward merging our two great companies.

Sincerely,

Bertrand Loy

President and Chief Executive Officer, Entegris

Forward Looking Statements

This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks and
uncertainties and are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1993, as amended and Section 21E of the Securities Exchange Act of 1934, as amended. Where a forward-looking statement expresses or
implies an expectation or belief as to future events or results, such expectation or belief is expressed in good faith and believed to have a reasonable basis. The words believe continue, could,
expect, anticipate, intends, estimate, forecast, project, should, may, will, would or the negative thereof and similar
expressions are intended to identify such forward-looking statements. These forward-looking statements are only predictions and involve known and unknown risks and uncertainties, many of which are beyond Entegris and Versum Materials
control. Statements in this communication regarding Entegris, Versum Materials and the combined company that are forward-looking, including projections as to the anticipated benefits of the proposed transaction, the impact of the proposed
transaction on Entegris and Versum Materials business and future financial and operating results, the amount and timing of synergies from the proposed transaction, and the closing date for the proposed transaction, are based on
managements estimates, assumptions and projections, and are subject to significant uncertainties and other factors, many of which are beyond Entegris and Versum Materials control. These factors and risks include, but are not
limited to, (i) weakening of global and/or regional economic conditions, generally or specifically in the semiconductor industry, which could decrease the demand for Entegris and Versum Materials products and solutions;
(ii) the ability to meet rapid demand shifts; (iii) the ability to continue technological innovation and introduce new products to meet customers rapidly changing requirements; (iv) the concentrated customer base; (v) the
ability to identify, effect and integrate acquisitions, joint ventures or other transactions; (vi) the ability to protect and enforce intellectual property rights; (vii) operational, political and legal risks of Entegris and Versum
Materials international operations; (viii) Entegris dependence on sole source and limited source suppliers; (ix) the increasing complexity of certain manufacturing processes; (x) raw material shortages and price increases;
(xi) changes in government regulations of the countries in which Entegris and Versum Materials operate; (xii) the fluctuation of currency exchange rates; (xiii) fluctuations in the market price of Entegris stock; (xiv) the
level of, and obligations associated with, Entegris and Versum Materials indebtedness; and (xv) other risk factors and additional information. In addition, material risks that could cause actual results to differ from
forward-looking statements include: the inherent uncertainty associated with financial or other projections; the prompt and effective integration of Entegris businesses and the ability to achieve the anticipated synergies and value-creation
contemplated by the proposed transaction; the risk associated with Entegris and Versum Materials ability to obtain the approval of the proposed transaction by their shareholders required to consummate the proposed transaction and the
timing of the closing of the proposed transaction, including the risk that the conditions to the transaction are not satisfied on a timely basis or at all and the failure of the transaction to close for any other reason; the risk that a consent or
authorization that may be required for the proposed transaction is not obtained or is obtained subject to conditions that are not anticipated; unanticipated difficulties or expenditures relating to the transaction, the response of business partners
and retention as a result of the announcement and pendency of the transaction; and the diversion of management time on transaction-related issues. For a more detailed discussion of such risks and other factors, see Entegris and Versum
Materials filings with the Securities and Exchange Commission, including under the heading Risks Factors in Item 1A of Entegris Annual Report on Form 10-K for the fiscal year ended
December 31, 2017, filed on February 15, 2018, and Versum Materials Annual Report on Form 10-K for the fiscal year ended September 30, 2018, filed on November 21, 2018 and in other
periodic filings, available on the SEC website or www.entegris.com or www.versummaterials.com. Entegris and Versum Materials assume no obligation to update any forward-looking statements or information, which speak as of their respective
dates, to reflect events or circumstances after the date of this communication, or to reflect the occurrence of unanticipated events, except as may be required under applicable securities laws. Investors should not assume that any lack of update to
a previously issued forward-looking statement constitutes a reaffirmation of that statement.

Additional Information about the Merger and Where to Find It

This communication does not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities or a solicitation of any vote or
approval. This communication relates to a proposed business combination between Entegris and Versum Materials. In connection with the proposed transaction, Entegris intends to file with the Securities and Exchange Commission (the SEC) a
registration statement on Form S-4 that will include a joint proxy statement of Entegris and Versum Materials that also constitutes a prospectus of Entegris. Each of Entegris and Versum Materials also plan to
file other relevant documents with the SEC regarding the proposed transaction. No offering of securities shall be made, except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended. Any
definitive joint proxy statement/prospectus (if and when available) will be mailed to stockholders of Entegris and Versum Materials. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT, JOINT PROXY STATEMENT/PROSPECTUS AND
OTHER DOCUMENTS THAT MAY BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY IF AND WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION. Investors and security holders will be able to obtain
free copies of these documents (if and when available) and other documents containing important information about Entegris and Versum Materials, once such documents are filed with the SEC through the website maintained by the SEC at
http://www.sec.gov. Copies of the documents filed with the SEC by Entegris will be available free of charge on Entegris website at http://www.entegris.com or by contacting Entegris Investor Relations Department by email at
irelations@entegris.com or by phone at 978-436-6500. Copies of the documents filed with the SEC by Versum Materials will be available free of charge on Versum
Materials website at investors.versummaterials.com or by phone at 484-275-5907.

Participants in the Solicitation

Entegris, Versum
Materials and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information about the directors and executive officers of Entegris is
set forth in Entegris proxy statement for its 2018 annual meeting of shareholders, which was filed with the SEC on March 28, 2018, and Entegris Annual Report on Form 10-K for the fiscal year
ended December 31, 2017, which was filed with the SEC on February 15, 2018. Information about the directors and executive officers of Versum Materials is set forth in its proxy statement for its 2019 annual meeting of shareholders, which
was filed with the SEC on December 20, 2018, and Versum Materials Annual Report on Form 10-K for the fiscal year ended September 30, 2018, which was filed with the SEC on November 21,
2018. Other information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the joint proxy statement/prospectus and other relevant
materials to be filed with the SEC regarding the proposed transaction when such materials become available. Investors should read the joint proxy statement/prospectus carefully when it becomes available before making any voting or investment
decisions. You may obtain free copies of these documents from Entegris or Versum Materials using the sources indicated above.